Accurate Tempo and the Metronome

Start all pieces by counting carefully, especially for beginners and youngsters. Children should be taught to count out loud because that is the only way to find out what their idea of counting is. It can be totally different from the intended one. You should understand the meter signature at the beginning of each composition. It looks like a fraction, consisting of a numerator and a denominator. The numerator indicates the number of beats per measure and the denominator indicates the note per beat. For example, 3/4 means that there are three beats per measure and that each beat is a quarter note. Typically, each bar contains one measure. Knowing the signature is essential when accompanying, because the moment that the accompanist starts is determined by the starting beat which the conductor indicates with the baton.
An advantage of HS practice is that you tend to count more accurately than HT. Students who start HT often end up with undetected mistakes in counting. Interestingly, these mistakes usually make it impossible to bring the music up to speed. There is something about wrong counting that creates its own speed wall. It probably messes up the rhythm. Therefore, if you run into problems with bringing it up to speed, check the counting. A metronome is very useful for this.
Use the metronome to check your speed and beat accuracy. I have been repeatedly surprised by the errors I discover when checked in this way. For example, I tend to slow down at difficult sections and speed up at easy ones, although I think it is actually the opposite when playing without the metronome. Most teachers will check their students' tempo with it. But it should be used only for a short time. Once the student gets the timing, it should be shut off. The metronome is one of your most reliable teachers -- once you start using it, you will be glad you did. Develop a habit of using the metronome and your playing will undoubtedly improve. All serious students must have a metronome.
Metronomes should not be over used. Long practice sessions with the metronome accompanying you are harmful to technique acquisition. This leads to mechanical playing. When the metronome is used for more than about 10 minutes continually, your mind will start to play mental tricks on you so that you may lose the timing accuracy. For example, if the metronome emits clicks, after some time, your brain will create anti-clicks in your head that can cancel the metronome click so that you will either not hear the metronome anymore, or will hear it at the wrong time. This is why most modern electronic metronomes have a light pulse mode. The visual cue is less prone to mental tricks and also does not interfere acoustically with the music. The most frequent abuse of the metronome is to use it to ramp up speed; this abuses the metronome, the student, the music, and the technique. If you must ramp up the speed gradually, use it to set the tempo, then turn it off and then keep on practicing; then use it again briefly when you increase the speed. The metronome is for setting the tempo and for checking your accuracy. It is not a substitute for your own internal timing.
The process of speeding up is a process of finding the appropriate new motions. When you find the correct new motion, you can make a quantum jump to a higher speed at which the hand plays comfortably; in fact, at intermediate speeds, neither the slow nor the fast motion applies and is often more difficult to play than the faster speed. If you happen to set the metronome at this intermediate speed, you might struggle at it for long periods of time and build up a speed wall. One of the reasons why the new motion works is that the human hand is a mechanical device and has resonances at which certain combinations of motions naturally work well. There is little doubt that some music was composed to be played at certain speeds because the composer found this resonance speed. On the other hand, each individual has a different hand with different resonance speeds, and this partly explains why different pianists choose different speeds. Without the metronome, you can jump from resonance to the next resonance because the hand feels comfortable at those speeds, whereas the chances of your setting the metronome at exactly those speeds is very low. Therefore, with the metronome, you are almost always practicing at the wrong speed. This is a great way to build any number of speed walls.
Electronic metronomes are superior to the mechanical ones in every respect although some people prefer the appearance of the old models. Electronics are more accurate, can make different sounds or flash lights, have variable volume, are less expensive, are less bulky, have memory functions, etc., while the mechanicals always seem to need rewinding at the worst possible times.